🚧Beam Design

📌A reinforced concrete beam must be proportioned according to its span (L) so that it safely carries loads without excessive bending or shear.

👉The image shows general guidelines, not exact code rules — final sizes must be based on structural design.

1. Beam Depth (H)

H = L / 12

📌The depth (height) of the beam should be about 1/12 of the span length.

Example: If span L = 6 m,
→ H ≈ 6000 / 12 = 500 mm

📌This ensures the beam can resist bending moments.

2. Beam Width (B)

B = L / 24

📌The width of the beam is generally half of its depth.

Example: If L = 6 m,
→ B = 6000 / 24 = 250 mm

This proportion keeps the beam stable and avoids cracking.

3. Longitudinal Reinforcement (Main Bars)

📌The top image shows red lines representing the tension reinforcement.

📌For long spans, beams tend to lift upward near supports due to negative moments.

📌Additional bars called “swings” or extra top bars are placed over supports.

📌Purpose:

✔ Controls cracking
✔ Handles negative bending moment
✔ Strengthens beam over supports

4. L/4 Reinforcement Zones

The bottom image shows   L/4 zones at both ends.

📌Why L/4?

🔗Negative bending moments occur near supports.

🔗So extra top bars must extend:

🔗L/4 from the support into the span.

Example: If L = 6 m,
L/4 = 1.5 m
→ Extra top bars must extend 1.5 m from each support.

5. Main Idea

📌A beam must be:

🔗Deep enough to resist bending

🔗Wide enough to ensure stability

🔗Properly reinforced at mid-span and supports

🔗Extra top bars are required at ends (L/4 region)

6. Important Note

The images provide general proportions only.

📌Actual design depends on:

🔗Load

🔗Span

🔗Material strength

🔗Building code (ACI / IS / BNBC etc.)

🔗Structural calculations are always required.


@etconp